The present invention relates to a method for preparing hydrocarbon cracking catalyst compositions, in particular relates to a method for preparing catalyst compositions which exhibit high catalytic activity, gasoline selectivity and depressed degree of formation of coke and further more display superior stability to heat and steam when used in catalytic cracking of heavy hydrocarbon containing large amounts of metals such as vanadium, nickel, iron, copper and the like.
Catalytic cracking of hydrocarbon originally aims at the production of gasoline. Therefore, catalysts used herein are demanded to exhibit high catalytic activity and gasoline selectivity. In addition, high thermal and hydrothermal stability is also one of the requisites for cracking catalysts because it is customary in the hydrocarbon catalytic cracking process to repeat many times the operation which comprises regenerating the deactivated catalysts which have been used in the reaction and thereafter employing the thus regenerated catalysts again in the reaction. Under these circumstances, the catalysts used in catalytic cracking of hydrocarbon have usually been improved by taking various means. For instance, the performance of the typical cracking catalyst composition which comprises dispersing a crystalline aluminosilicate in an inorganic oxide matrix has been improved by introducing a rare earth component in said composition by means of ion exchange, impregnation or the like or by dispersing a rare earth exchanged crystalline aluminosilicate in the matrix. And, these improvements have achieved considerable results, and the thus improved cracking catalyst has displayed its performance to a satisfactory degree so far as the heavy hydrocarbon feed oil used is not low grade too much, in other words does not contain large amounts of metallic contaminants.
In recent years, however, it is becoming necessary with deterioration of the oil situation to employ low grade heavy hydrocarbon oils such as residual oils containing large amounts of metals such as vanadium, nickel and the like as a feed stock for catalytic cracking processes without any pre-treatment. However, in case the low grade oil of this type is subjected to catalytic cracking processes using a conventional catalyst, the catalyst has been poisoned severely by metallic contaminants contained in the feed oil, and consequently the primary purpose of catalytic cracking can not be accomplished because the catalytic activity and gasoline selectivity of said poisoned catalyst are destroyed and the amounts of coke and gases generated increase markedly. Accordingly, when subjecting the low grade heavy hydrocarbon containing a large amount of metallic contaminants to catalytic cracking, there have usually been employed the way of suppressing the deposit amount of metal of the catalysts by increasing the amount of catalyst used, the way of passivating the metal by adding an antimony compound in the feed oil, the way of prehydrotreating a feed oil for removing the metallic contaminants and the like contained in the feed oil to some extent and then subjecting same to catalytic cracking, and the like. However, these conventional ways can never be recommended because the running cost increases.
Some of the inventors of this invention, M. Ogata and T. Ida, Have previously proposed, together with Y. Nishimura, a method for preparing hydrocarbon cracking catalyst compositions which can obtain not only the gasoline fraction but also the intermediate fraction such as kerosene or the like in a high yield (see Japanese Laid Open Patent Application No. 163439/1983 Specification). This method comprises spray drying an aqueous slurry containing a flash calcined alumina obtained by contacting the aluminum hydroxide prepared by Bayer's process with a hot air for a short time, kaolin, a precursor of a siliceous matrix and a crystalline aluminosilicate.
We have found that the catalyst obtained by introducing a rare earth component to the catalyst composition prepared by the above mentioned method exhibits a superior performance as the cracking catalyst in treating the low grade heavy hydrocarbon oil containing large amounts of metallic contaminants, in marked contrast to the catalyst of the same kind but free from said flash calcined alumina.